1. Technical Field
This invention pertains to the manufacture of polyurethane-elastomers polymerized with an aromatic diamine chain extending agent.
2. Description of the Prior Art
Polyurethane-urea elastomers have been widely used in the industry for the manufacture of molded parts, suitably for automobile grilles and bumpers, support mountings for headlights and tail lights and a host of other manufactured products.
Polyurethane urea elastomers for these applications typically are formed by reacting an organic polyisocyanate with a compound having molecular weight between 400-10,000 containing at least two Zerewitenoff active hydrogen atoms and an aromatic diamine chain extending agent. The aromatic diamine chain extender is incorporated into the polyurethane formulation to improve the structural stability, tensile strength, recoil elasticity and permanent elongation of the resulting resin. As is known, though, aromatic diamines containing primary amine functionality are highly reactive with isocyanate terminated polyurethane prepolymers formed from organic polyisocyanates and polyol prepolymers and are unsuited for molding large parts. For example, a reaction mixture comprising an isocyanate terminated prepolymer and toluene diamine as a chain extending agent must be formulated and molded immediately otherwise the reaction mixture may gel prior to molding.
Two techniques have been utilized to reduce the reactivity of aromatic diamines in order to formulate polyurethane area elastomer molding formulations. One technique involves incorporating organo substituents on the aromatic ring which sterically hinder the amine functionality; the other is to incorporate substituents on the aromatic ring which electronically deactivate the aromatic ring. Representative patents illustrating steric hinderance of the functionality as a mechanism for reducing activity are as follows.
U.S. Pat. Nos. 3,428,610 and 4,218,543 disclosure aromatic diamines having alkyl groups in the ortho position to the amine as e.g., diethyl toluene diamine, chain extenders for polyurethane. As noted in the '543 patent, many aromatic amines are not suited for reaction injection molding (RIM) of polyurethane urea forming elastomers because the pot life of the mixture is too short. The incorporation of alkyl groups ortho to the amine groups reduces the reactivity of the aromatic amine and thus makes them suited for many molded operations.
U.S. Pat. No. 3,846,351 discloses the utilization of secondary aromatic alkyl diamines as chain extenders and foam catalysts for polyurethane-urea elastomer forming compositions. N,N'-disec-butyl-p-phenylenediamine is one example of an amine having chain extending and catalytic activities. In this case, the primary amine functionality is converted to secondary amine functionality, which can affect the tensile modulus of the elastomer.
U.S. Pat. No. 3,285,879 discloses the utilization of N-monoalkyl aromatic diamines as a chain extending agent for polyurethane-urea elastomers. Two of the advantages stated by the patentee is that the N-monoalkyl aromatic diamines impart a practical pot life for the urethane-urea elastomer formulations and result in producing a soft, highly flexible rubbery product. An example of monoalkyl aromatic diamine is N-octyl-p-phenylenediamine. The procedure utilized here for reducing reactivity is similar to the '351 patent.
The second technique for reducing activity of an aromatic amine is through electronic deactivitation of the ring. One of the better known aromatic diamine chain extenders utilizing ring deactivation to extend pot life to urethane-urea elastomer formulations is methylene-bis(orthochloroaniline) (MOCA). MOCA, of course, uses a chlorine atom to deactive the ring. Although MOCA has been widely used in the past it is finding disfavor in the industry because it is suspected of having carcinogenic characteristics. Other types of chain extenders have been utilizing electronic deactivation are:
U.S. Pat. No. 3,736,350 discloses aromatic diamines containing ester and halogen or alkoxy radicals. A representative structure follows: ##STR1## where R is an alkyl radical and X is an alkoxy radical having from 1 to 4 carbon atoms or a halogen atom. Representative chain extenders include 4-methoxy-3, 5-diaminobenzoic acid methylester; 4-aminobenzoic acid-(3'-chloro-4'-amino)-phenyl ester; and 4,4'-dichloro-3,3'-diamino diphenyl; carbonate.
U.S. Pat. No. 4,133,943 suggests various aromatic diamino carboxylic acid esters as chain extenders for urethane urea elastomers. A representative structure is ##STR2## where R has aliphatic or cycloaliphatic and X is a halogen atom, alkoxy or trifluoromethyl radical.
U.S. Pat. No. 4,222,955 discloses various substituted aromatic diamines which are 3,5-diamino-4 tert-alkylbenzoates and 3,5-diamino-4 tert-alkylbenzonitriles. The patent indicates that the benzoate ester deactivates the ring to provide a longer pot life. Examples of chain extender agents are methyl 3,5-diamino-4-t-butyl benzoate and methyl 3,5-diamino-4-t-butyl benzonitrile.